A check valve can be located in the intake passage of an engine leading to a cylinder to obstruct back-flow of fluid out of the cylinder into the intake passage. In such an arrangement, a trapped volume is defined by the portion of the intake passage between the check valve and an intake valve seated in the intake passage between the check valve and cylinder.
A port can be located on the intake passage so that the port communicates with the trapped volume, and a secondary passage can be connected to the port allowing a secondary air flow into the trapped volume increasing the pressure therein.
A control valve can be connected to the secondary passage to enable adjustment of its flow area. The ability of such a control valve to rapidly adjust the flow area of such a secondary passage appears, however, to be limited. This can limit improvements in engine performance produced by the secondary air flow, particularly if the operating condition of the engine changes rapidly since the optimum pressure in the trapped volume can vary depending on the operating condition of the engine. Improvements in engine performance during idle and light load operation can be particularly limited because of the sensitivity of the engine performance to trapped volume pressure during such operation.
A check valve can be located upstream of each cylinder of a multi-cylinder engine thereby defining a respective trapped volume for each cylinder. Such engines can include a secondary passage connected to each trapped volume for providing secondary air thereto. Such secondary passages can be supplied from a single duct having a control valve. The ability to rapidly and accurately adjust such a control valve appears, however, to be limited.
Moreover, the single duct allows unrestricted communication between secondary passages leading to trapped volumes being pressurized, and other secondary passages leading to cylinders into which air is flowing. The reduced pressures in the other secondary passages can cause pressure reductions in the secondary passages leading to the trapped volumes being pressurized thereby reducing the pressurization therein. The control valve in the duct can restrict the secondary air flow into the secondary passages reducing the effect of the secondary air flow in restoring the pressure therein.